FONDA — Throwback to the fall: a man walked in moments before a local library trustees meeting in Fonda village and handed over a $50,000 check, nearly matching the small community institution's public funding. And then he left. Members of the board started crying. "We didn't even escort him out the door," said Linda Bell, associate director of the Frothingham Free Library, at a Monday event commemorating the donation. "We were in such shock that we because we were all like, 'I can't believe this just happened to us.'" The out-of-the-blue figure was village resident Jerry Collins, a retired Frontier…